Bridged network system with traffic resiliency upon link failure

ABSTRACT

A bridged network system ( 10, 10 ′) is described comprising a plurality of nodes (N 1 -N 7 ). Each node in the plurality of nodes is coupled to communicate with at least one other node in the plurality of nodes. The plurality of nodes comprise a bridge network between external nodes located externally from the plurality of nodes. Each node of the plurality of nodes is operable to perform the steps of receiving a packet ( 20, 20 ′), wherein the packet comprises a route indicator field, and responsive to the packet being received prior to a time of failure along a communication link between two of the plurality of nodes, transmitting the packet along a first route in the system to another node in the plurality of nodes. Conversely, each node of the plurality of nodes is also operable to perform the step of, responsive to the packet being received after a time of failure along a communication link between two of the plurality of nodes and in response to the route indicator field, transmitting the packet along a second route in the system to another node in the plurality of nodes, wherein the second route differs from the first route and is identified prior to the time of failure.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit, under 35 U.S.C. §119(e)(1), of U.S.Provisional Application No. 60/419,756, filed Oct. 18, 2002, andincorporated herein by this reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

BACKGROUND OF THE INVENTION

The present embodiments relate to computer networks and are moreparticularly directed to a bridged network system in which trafficresiliency is provided by quickly switching traffic to a pre-identifiedroute upon a link failure.

A bridged network is one type of network that has found favor in variousapplications in the networking industry, and for various reasons. Abridged network in many approaches is based on Ethernet switches thatare Layer 2 switches, and the basic principle of operation of such anetwork includes learning of MAC addresses, broadcasting of unknown MACaddresses, and use of a Spanning Tree Protocol to provide loop-freeoperation. With Ethernet used as a technology in a bridged network, itis a widely used and cost effective medium with numerous interfaces andcapable of communications at various speeds up to the Gbps range. Withthe use of such networks, mechanisms for routing and re-routing traffichave evolved in the instance of a communication failure between bridgednetwork nodes. In this context and throughout this document, the term“node” includes what are referred to in the art as switches or bridgesand is known as a device for communicating a block of data. The datablock is often referred to as a packet or frame and it is transmitted inthe bridged network from one node to another node that is connected tothe transmitting node via a physical line referred to as the link andaccording to a protocol. One common protocol that is particularly usedto provide loop-free operation and resilience is the spanning treeprotocol, with a specific type of that protocol being known as the rapidspanning tree protocol (“RSTP”). The RSTP provides various aspects,where one is to provide a so-called spanning tree along which datapackets pass. The spanning tree is logically defined to include a rootnode that transmits via logical links to other intermediate nodes andultimately to an endpoint node. In the spanning tree configuration, ifthere is a failure along the tree then the RSTP provides communicationsamong the various nodes so as to “re-converge” to a new spanning tree(i.e., a new different set of logical links), and thereafter traffic isrouted according to the new spanning tree. Each spanning tree in theprior art has the characteristic that it prevents loops from occurringin response to broadcast transmissions, that is, it breaks whatotherwise could be a loop in transmissions and thereby prevents a samenode from receiving duplicate packets along different links in the samenetwork.

While the spanning tree protocol has proven beneficial in someimplementations, it also may provide certain drawbacks. For example, theRSTP may be relatively slow to re-converge to a new tree following afailure because the protocol relies on exchange of bridge protocol dataunits (“BPDUs”) between the nodes and the root. Hence, depending on thetopology, fast re-convergence may not be possible and the re-convergencetimes can take up to two to three seconds. For some applications this isnot an acceptable figure. Further, during operation under RSTP and inresponse to a failure, MAC addresses need to be flushed and re-learnedwhich is an expensive operation. Consequently, these approaches are notbeing viewed as carrier-grade technology.

In view of the above, there arises a need to address the drawbacks ofthe prior art, as is accomplished by the preferred embodiments describedbelow.

BRIEF SUMMARY OF THE INVENTION

A bridged network system is described comprising a plurality of nodes.Each node in the plurality of nodes is coupled to communicate with atleast one other node in the plurality of nodes. The plurality of nodescomprise a bridge network between external nodes located externally fromthe plurality of nodes. Each node of the plurality of nodes is operableto perform the steps of receiving a packet, wherein the packet comprisesa route indicator field, and responsive to the packet being receivedprior to a time of failure along a communication link between two of theplurality of nodes, transmitting the packet along a first route in thesystem to another node in the plurality of nodes. Conversely, each nodeof the plurality of nodes is also operable to perform the step of,responsive to the packet being received after a time of failure along acommunication link between two of the plurality of nodes and in responseto the route indicator field, transmitting the packet along a secondroute in the system to another node in the plurality of nodes, whereinthe second route differs from the first route and is identified prior tothe time of failure.

Other aspects are also described and claimed.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 a illustrates a block diagram of a system 10 into which apreferred embodiment may be implemented.

FIG. 1 b illustrates system 10, but with an additional set of logiclinks between the system nodes and to be used to route packets in abypass mode.

FIG. 1 c illustrates the flexibility of a preferred embodiment inpermitting a bypass path to route beyond a single spanning tree link.

FIG. 2 illustrates a packet format 20 according to the preferredembodiment of FIGS. 1 a through 1 c.

FIG. 3 illustrates a system 10′ as an alternative to system 10 describedabove, where system 10′ routes packets across alternative pre-computedsets of logic links.

FIG. 4 illustrates a packet format 20′ according to the alternativepreferred embodiment of FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 a illustrates a block diagram of a system 10 into which thepreferred embodiments may be implemented. System 10 generally representsa bridged network such as an Ethernet network and that includes a numberof network nodes N₁ through N₇. Such nodes are sometimes described asedge nodes or core nodes based on their location in the network. Edgenodes are so named as they provide a link to one or more nodes outsideof the Ethernet network and, hence, logically they are located at theedge of the network, whereas core nodes are inside the edges defined bythe logically perimeter-located edge nodes. An Ethernet network is oftena publicly accessible network that provides a common domain, typicallyunder the control of a single administrator, such as an Internet ServiceProvider (“ISP”). Ethernet may be used to connect to the global Internetand to connect between geographically separated sites, such as betweendifferent locations of a business entity. Also, the Ethernet network isoften shared among different customer virtual local area networks(“VLAN”), where these networks are so named because a first VLAN isunaware of the shared use of the Ethernet network by one or moreadditional VLANs. In this manner, long-standing technologies andinfrastructures may be used to facilitate efficient data transfer.

Nodes N₁ through N₇ include various aspects as known in the art, such asoperating to send a packet as a source or to receive a packet as adestination. Further, and as also known in the art, system 10 istypically coupled with stations or nodes external from system 10, suchas may be implemented in the global Internet or at remotely locatednetworks, such as at different physical locations of a business entity.These external nodes can communicate packets with system 10. Forexample, one such node external from, but coupled to, node N₁ maythereby communicate a packet to node N₁. In this example, since thepacket enters the domain of system 10 through node N₁, then node N₁ isreferred to as an ingress node. Further, once that packet is soreceived, it may be forwarded on through various paths of system 10, andultimately it will reach one of the other nodes and then may passoutward of system 10. For example, the packet may reach node N₄, whichmay then communicate that packet also external with respect to system10, by transmitting the packet onward via a link from node N₄ to such anexternal node. In this way, since the packet exits the domain of system10 through node N₄, then node N₄ is referred to as an egress node. Oneskilled in the art should appreciate that the number of nodes shown inFIG. 1 a is solely by way of example and to simplify the illustrationand example, where in reality system 10 may include any number of suchnodes. Further, one skilled in the art should also appreciate that eachsuch node may be readily constructed and programmed using to varioushardware/software/firmware to provide the operation and functionalitydescribed in this document.

In one aspect of a preferred embodiment, system 10 operates according toa known spanning tree protocol, such as the above-introduced RSTP.Toward this end, in FIG. 1 a, a number of logical links are shown insystem 10 as solid lines between various nodes, connecting various ofthe nodes to one another for the sake of routing packets along suchlinks. The logical links in their entirety form a spanning tree amongthe nodes, that is, a defined connectivity for packet flow. Morespecifically, according to the RSTP, during the operation of system 10and according to known IEEE standards, control messages are exchangedbetween each node to one of the nodes which is designated as the root.Further during this process, each node establishes its own forwardingtable, where that table indicates to the respective node that for apacket received on a given port for the node, the node is then to routethe packet to a corresponding port based on the destination MAC addressin the packet. Accordingly, with each node having such a forwardingtable, a logical link is established from that node to at least oneother node, thereby giving rise to the illustration of logical links inFIG. 1 a. Further in this regard, in FIG. 1 a, each node is shown tohave at least one port, and for sake of convention each such port islabeled with the letter “P” and is followed by a number corresponding tothe same node. For example, node N₁ has a port P1 _(x). The subscript“x” for each such node is added to distinguish multiple ports at thesame node. For example, node N₁ only has one port and, thus, it islabeled port P1 ₁, while node N₂ has two ports, P2 ₁ and P2 ₂. Given thespanning tree logical links and the preceding conventions, then theconnectivity in FIG. 1 a is as shown in the following Table 1:

TABLE 1 Node connected to by port N₁ N₂ P1₁ N₂ N₁ P2₁ N₂ N₃ P2₂ N₃ N₂P3₁ N₃ N₄ P3₂ N₄ N₃ P4₁ N₄ N₅ P4₂ N₅ N₄ P5₁ N₅ N₆ P5₂ N₆ N₅ P6₁ N₆ N₇P6₂ N₇ N₆ P7₁Note that Table 1 is provided to demonstrate the connections in FIG. 1a, but it is not intended to represent an actual forwarding database orforwarding table maintained by any particular node in system 10.

Given the preceding and under a preferred embodiment, when no networkfailure has occurred for system 10, then each node consults itsrespective forwarding table to route packets in a typical spanning treefashion. As an example, assume that node N₂ receives a packet that has adestination MAC address to a node that is external from and connected tonode N₄. In other words, in the example, node N₄ is considered an egressnode in that the packet will exit the domain defined by system 10 bybeing transmitted outward from that domain via node N₄. Returning tonode N₂, it consults its forwarding table to determine, based on thedestination MAC address in the packet, the port of node N₂ on which thepacket should be transmitted. Given the spanning tree logical linksshown in FIG. 1 and Table 1, node N₂ will determine that its port P2 ₂provides a connection toward the destination MAC address and, hence,node N₂ thereby transmits the received packet via that port. Continuingwith this example, the transmitted packet will then be received by nodeN₃ at its port P3 ₁. Node N₃ then consults its forwarding table, todetermine a transmit port that corresponds to the destination address inthe packet, which recall is a destination that is external from node N₄.Accordingly, node N₃ identifies its port P3 ₂ as the desired port, andit transmits the packet via that port. Completing the example, node N₄then receives, via its port P4 ₁, the packet from node N₃. From thedestination address in the packet, node N₄ determines from itsforwarding table that its port P4 ₃ provides connectivity toward thedestination node (not shown) and, hence, node N₄ transmits the packetoutward from its port P4 ₃.

If system 10 were implemented according to the prior art, then upon afailure of one of the links in FIG. 1 a, then a dynamic and automatedtechnique is performed whereby a new spanning tree is defined among itsvarious nodes. Particularly, in such a case, additional control messagesare communicated among the various nodes so as to identify the failedlink and to establish a new spanning tree. During this transition time,each node is required to flush information out of its respectiveforwarding table, and in response to the new control messages eachforwarding table is re-built, which is sometimes referred to as are-learn procedure. When the forwarding table is complete for each node,the system is said to have re-converged to a new spanning tree. Asdiscussed earlier in the Background Of The Invention section of thisdocument, however, this procedure takes time, and in someimplementations may be disadvantageous or even prohibitive. Accordingly,the following discussion demonstrates how system 10, according to onepreferred embodiment, provides an alternative manner of responding to alink failure and that improves upon drawbacks of the current state ofthe art.

FIG. 2 illustrates a packet format 20 according to a preferredembodiment and for use in connection with system 10 of FIG. 1 a. Packetformat 20 includes various fields as known in the Ethernet art, and onlysome of which are shown by way of example. These fields include a sourceaddress field 20 ₁, a destination address field 20 ₂, a length field 20₃ and a data payload field 20 ₄. Other fields, although not shown, maybe included as also known in the art, such as a preamble and a packet(or frame) start field. According to the preferred embodiment, however,packet format 20 includes an additional field 20 ₅, referred tohereafter as a link type field 20 ₅. Link type field 20 ₅ is so namedbecause, as shown below, the state of the field indicates the type oflink on to which the packet is routed, with one state in field 20 ₅(e.g., 0) indicating a spanning tree link and another state in field 20₅ (e.g., 1) indicating a bypass link along system 10. In the preferredembodiment, link type field 20 ₅ is a one-bit field and it iscontemplated that it could be a bit provided as an addition to existingEthernet frames or, alternatively, it could be a bit that is already inthe Ethernet frame yet where the function of that bit is changed to beconsistent with the functionality described in this document as relatingto link type field 20 ₅. In either event, and for reasons more clearbelow, note that link type field 20 ₅ is only needed to serve a functionwithin the domain of system 10 and, thus, if desirable, that field maybe stripped from packet format 20 prior to transmitting the packetexternally from system 10.

FIG. 1 b returns to an illustration of system 10, but for reasons moreclear below it illustrates a set of logic links between the system nodesand to be used when link type field 20 ₅ of FIG. 2 is set to the bypassmode, where these logic links are shown with solid lines between variousnodes. For the sake of later reference, each solid line link between twonodes in FIG. 1 b is referred to as a bypass link. Also, for sake ofcontrast, the spanning tree logic links of FIG. 1 a are also shown inFIG. 1 b, but they are shown using dashed lines to distinguish then fromthe bypass links of FIG. 1 b. In general and as shown below, each bypasslink may provide a backup or bypass function in the event of a failureof a spanning tree link. The specific connectivity of the bypass linksof FIG. 1 b are as shown in the following Table 2:

TABLE 2 node connected to by port N₁ N₇ P1₂ N₂ N₇ P2₃ N₂ N₆ P2₄ N₃ N₆P3₃ N₃ N₅ P3₄ N₄ N₅ P4₂ N₅ N₄ P5₁ N₅ N₃ P5₃ N₆ N₃ P6₄ N₆ N₂ P6₃ N₇ N₂P7₃ N₇ N₁ P7₂

In one preferred embodiment, the bypass links of system 10, such asthose shown in Table 2, are established statically given knowledge ofthe network topology and preferably before a link failure occurs. Moreparticularly, for each node, a table referred to herein as a bypasstable is created, and static port to port information is provided inthat table for purposes of routing packets along the bypass links. Forexample with respect to node N₆, its bypass table correlates its port P6₃ with its port P6 ₄ when bypass communications are to occur, that is,for a packet received by node N₆ at port P6 ₃, it is to be transmittedby node N₆ via port P6 ₄. For reasons further discussed later, givensuch an association, if the node receives a packet of one of these twoassociated ports and the packet is indicated to be routed via a bypasslink, then the packet is then transmitted by the node out of the otherand associated node, without reference to the destination MAC address inthe packet. In the current example, therefore, and unlike the prior artforwarding table used in a spanning tree network and which associates anoutgoing port with an in-packet destination MAC address, in thepreferred embodiment the bypass table associates two ports at the samenode. As a final observation, note in the example of FIG. 1 b that manyof the protection links are defined so that a path is created across twobypass links that permits a packet to be routed around a single spanningtree logical link. For example, for the spanning tree logical linkbetween nodes N₁ and N₂, there is an alternative path defined by a firstbypass link from node N₁ to node N₇ and a second bypass link from nodeN₇ to node N₂. As another example, for the spanning tree logical linkbetween nodes N₂ and N₃, there is an alternative path defined by a firstbypass link from node N₂ to node N₆ and a second bypass link from nodeN₆ to node N₃. Other examples, as well as the operation with respect tothese paths, will be further appreciated from the remaining discussion.

The operation of system 10 according to one preferred embodiment is nowdescribed with reference to both FIGS. 1 a and 1 b. By way ofintroduction, recall that packets may be routed in system 10 along aspanning tree link or along a bypass link, where recall also that thedestination is preferably triggered in part by the link type field 20 ₅introduced above in connection with FIG. 2. Each of these alternativesis discussed below.

When packets are routed to the spanning tree links in system 10, system10 operates according to known spanning tree operation, with theexception that each packet also includes a link type field 20 ₅ set to astate (e.g., 0) that thereby indicates that the packet is to be routedto a spanning tree link. Accordingly, as any node in system 10 receivessuch a packet, it routes the packet according to spanning treeoperation. Thus, each node in system 10 that receives a packetdesignated for a spanning tree link consults its forwarding table todetermine which port is associated with the external destination MACaddress shown in the destination address field 20 ₂ of the packet. Forsake of later comparison, this association is as shown as the followingAssociation 1:external destination MAC address→transmit port  Association 1Following the look up of Association 1, then the node transmits thepacket via the indicated transmit port to the next spanning tree link.In other words, under such operation, packets are routed along the linksshown in FIG. 1 a. For example, assume that node N₂ receives, at port P2₁ as a receipt port, a packet with an external destination MAC addressthat is external from and accessible via node N₅. In response, node N₂locates in its forwarding table the port that corresponds to theexternal destination address that is external from and accessible vianode N₅; as shown in FIG. 1 a, in this case the transmit port is port P2₂. Accordingly, node N₂ transmits the packet via its port P2 ₂ as atransmit port and thereby transmits the packet outward via that port.

When a failure occurs in a link in system 10, that failure is detectedaccording to known protocols. However, as an enhancement in a preferredembodiment, in response to the failure detection, a node within system10 changes the state of link type field 20 ₅ so that each packet sochanged will be routed along a bypass link, where recall by way ofexample that a binary value of 1 in link type field 20 ₅ causes thiseffect. Further, when a node within system 10 receives a packet with abinary value of 1 in its link type field 20 ₅, the receiving node doesnot consult its forwarding table for purposes of further routing thereceived packet, but instead it consults its bypass table to determinethe next route for the received packet. As an illustration of thepreceding, for such a bypass-designated packet, its route is no longeraccording to the spanning tree links as illustrated generally in FIG. 1a, but instead it is according to the bypass links as illustratedgenerally in FIG. 1 b. Thus, as an example, assume in FIG. 1 a that afailure occurs in the spanning tree logical link between nodes N₂ andN₃, and consider once more the example of a packet that was intended totraverse system 10 from node N₂ and with a destination address to a nodethat is connected externally with respect to node N₄. In the prior art,such a failure would be responded to by nodes immediately flushing theirrespective forwarding tables, with a delay or drop in packettransmission as the network would re-converge on a new spanning tree. Incontrast, however, according to one preferred embodiment, in such acase, the nodes adjacent the failure become quickly aware of the failure(through known protocol) and they are able to mark any received packetwith a value of 1 (i.e., bypass) in link type field 20 ₅ of the packet.For example, assume that node N₂ receives a packet via a spanning treelink on its port P2 ₁ while at the same time node N₂ has notice of afailure in the adjacent spanning tree link between nodes N₂ and N₃. Inresponse, response, node N₂ changes the state of link type field 20 ₅ inthe received packet from a value of 0 to a value of 1; at the same time,note in the preferred embodiment that node N₂, as a node adjacent thefailure, delays the flushing of addresses in its forwarding tablebecause otherwise it will have to broadcast. In an alternative approach,however, a node prior to one adjacent the failure, such as node N₁ inthe present case, may change the state of link type field 20 ₅ in areceived packet from a value of 0 to a value of 1, in which case thedelayed flushing is not required. In any event, returning to the presentexample and with type field 20 ₅ now set to a value of 1, node N₂consults its bypass table to determine, for the packet now in the bypassmode, the appropriate transmit port. In other words, the association ofthe bypass table is as shown in the following Association 2:receipt port→transmit port  Association 2With respect to the actual association result for the present example,FIG. 1 b indicates the two possibilities in this case, namely, ports P2₃ and P2 ₄; assume further in the present example that the bypass tableindicates a transmit port of P2 ₄ for a receipt port of P2 ₁.Accordingly, in the present example, node N₂ transmits the packet alongits transmit port P2 ₄, which as seen in FIG. 1 b thereby transmits thepacket to node N₆. Note also in this regard that the transmitted packetis thereby routed away from the spanning tree logical link failurebetween nodes N₂ and N₃.

Continuing with a bypass packet as described above, additionalconsiderations are taken in one preferred embodiment when such a packetis received by a node and already has been so designated. In otherwords, in the preceding discussion, node N₂ was the first node to markthe packet as a bypass packet (i.e., by changing the state of link typefield 20 ₅ from 0 for a spanning tree link to 1 for a bypass link), andthat packet was forwarded to a next node, which in the example is nodeN₆. The next receiving node, therefore, receives the packet as alreadybeing indicated as a bypass packet. In the present example, this is nodeN₆. In response to receiving a packet with a link type field 20 ₅ set to1, the receiving node (e.g., node N₆) consults its bypass table. Also inthis regard, in one preferred embodiment the bypass table for each nodeincludes sufficient information so that such a receiving node maydetermine based on its receipt port the location of the failed link andwhether the receiving node is adjacent (i.e., directly connected to) thefailed link; in the present example, therefore, node N₆ may determine,from receiving a bypass packet on its port P6 ₃, that the correspondingspanning tree link that has failed is the spanning tree logical linkbetween nodes N₂ and N₃. Further, node N₆, from its bypass table, isinformed that it is not adjacent this link. In response, node N₆identifies a transmit port corresponding to the port at which the nodereceived the packet (i.e., the receipt port), and node N₆ transmits thebypass packet via that transmit port; in the present example, assume fora receipt port of P6 ₃ that the corresponding transmit port is port P6₄. Thus, the packet is transmitted by node N₆ via port P6 ₄ to node N₃.

Continuing with a bypass packet as described above, additionalconsiderations are taken in the preferred embodiment when such a packetis received by a node and already has been so designated, and furtherwhere the receiving node is adjacent the failed link. Continuing thenwith the preceding example, recall that a failure occurred in a spanningtree link between nodes N₂ and N₃, node N₂ changed link type field 20 ₅in the packet to a value of 1, and the packet was routed to node N₆which in response consulted its bypass table (because of the set linktype field 20 ₅) and routed the packet to node N₃.

Node N₃, therefore, represents a node that receives a bypass packet andthat is adjacent (i.e., directly connected to) a link failure. Accordingto one preferred embodiment, the response of such a node may be one oftwo approaches. In a first approach, the node changes the stated of thelink type field 20 ₅ of the packet back to a value (e.g., 0) that willcause the packet thereafter to be routed in a manner comparable to theprior art spanning tree protocol. Further in this case, the nodeoperates according to the spanning tree protocol by consulting itsforwarding table, thereby transmitting the packet further through system10 at a transmit port that corresponds to the external destinationaddress in the field 20 ₂ of the packet (i.e., Association 1). In thepresent example, therefore, node N₃ determines, as shown in the spanningtree logical link in FIG. 1 a, that the packet is to be transmitted viaits port P3 ₂. Also, after the packet transmission by node N₃, andassuming no additional link failures, then the packet will be processedusing the same procedures and rules as used in the prior art RSTP.Further, note that if the forwarding table at node N₃ already has beenflushed due to the already-detected failure between nodes N₂ and N₃,then packets are being broadcast exactly as mandated by the RSTP. Notealso from the preceding that this first approach therefore requires thata receiving node have knowledge that it is adjacent the already-detectedspanning tree logical link failure. In an alternative and secondapproach, however, after a packet has been indicated as a bypass linkpacket, then that status may remain in effect as the packet traversesthe remainder of its path in the domain illustrated by system 10. Thus,in the present example and again considering node N₃ receiving a packetwith a link type field 20 ₅ set to 1, then the node consults its bypasstable and transmits the packet via the transmit port that corresponds tothe receipt port (i.e., Association 2). In the bypass route shown inFIG. 1 b, therefore, node N₃ determines that it received the packet atreceipt port P3 ₃ and its bypass table indicates a correspondingtransmit port of port P3 ₄. Thus, node N₃ transmits the packet alongport P3 ₄ to node N₅, which receives the packet at its receipt port P5₃. Completing the second and alternative approach, node N₅ thereforealso receives a packet with a link type field 20 ₃ set to 1, and inresponse node N₅ consults its bypass table. Accordingly, the bypasstable correlates the receipt port P5 ₃ with the transmit port P5 ₁, sonode N₅ then transmits the packet to node N₄, which is the egress nodefor the domain represented by system 10. Note also that in the preferredembodiment, node N₄, as the egress node, removes link type field 20 ₅from the packet as that field is not needed once the packet exits thedomain of system 10.

According to a preferred embodiment as has been described, twopost-failure-detection alternatives are contemplated: (1) in one apacket is only partially routed as a bypass link packet within system 10until the packet is beyond the location of the failure; (2) in anotherthe packet is fully routed as a bypass link packet within system 10until an egress node is reached. In either case, as either of thesealternatives is routing packets, it is further contemplated that system10 uses a protocol, such as a known protocol, to re-converge to a newspanning tree that contemplates isolating the detected existing failure.Note, however, that this re-convergence time does not significantlydelay or drop packets as is the case in the prior art because packettransmissions are permitted to occur simultaneously with there-convergence to a new spanning tree. Further, once the new spanningtree is fully converged, then each packet may be returned to a spanningtree link designation in its link type field 20 ₅, unless of course afailure occurs in a logical link of the new spanning tree, in which casethe above-described preferred embodiment may be implemented inconnection with the failure of the newer spanning tree. Lastly, notethat during re-convergence there is the possibility of a loop, that is,the transmission of a packet to the same node according to bothtechniques, that is, one along a spanning tree link and one along abypass link, where both of these packets may then be received by adestination node within system 10. However, further due to the preferredembodiment, such packets will have differing values in the respectivelink type field 20 ₅ of each such packet, thereby making themdistinguishable and resolvable at the receiving node.

FIG. 1 c illustrates an additional aspect of flexibility of thepreferred embodiment and once again depicts system 10. However, in FIG.1 c, an alternative set of bypass logic links are shown to demonstratethat the preferred embodiment is not limited to protecting a singlespanning tree logical link with two bypass links. Also, for sake ofcontrast, the logic links of FIG. 1 a are also shown in FIG. 1 c, butthey are shown using dashed lines to distinguish the from the bypasslinks of FIG. 1 c. The specific connectivity of the bypass links of FIG.1 c are as shown in the following Table 3:

TABLE 3 node connected to by port N₁ N₆ P1₃ N₆ N₁ P6₅ N₆ N₃ P6₆From FIG. 1 c and Table 3, one skilled in the art will appreciate thatbackup links can be provided not only to protect a single spanning treelink, but also a series of spanning tree links, depending on whether thenetwork nodes can support this operation. For example, FIG. 1 cillustrates an example where the bypass links are provided to protectthe combination of spanning tree links from node N₁, to node N₂, to nodeN₃. Hence, the preferred embodiment may be used to open backup pathsover parts of the network to provided added security and can beimplemented and provided separately.

As another observation with respect to the preferred embodiment asdemonstrated in FIGS. 1 a and 1 b, this approach may be used to emulate1+1 and 1:1 protection for certain applications. More specifically, inthe case of 1+1 protection, there is required two live paths; using thepreferred embodiment, a primary path may be provided for spanning treedesignated packets (i.e., link type field 20 ₅ equal to 0) and asecondary path may be concurrently provided by bypass designated packets(i.e., link type field 20 ₅ equal to 1), assuming that all the nodes areconformant. Thus, using this approach, frames may be sent on both paths(one set in the solid lines in FIG. 1 a, one set in FIG. 1 b). Further,in case of a failure, the RSTP mechanism associated with the primarypath re-converges and finds another primary path, and then a signalingcould indicate to duplicate the frames on the backup paths (for everylink). In the case of 1:1, packets are not being sent automatically,however in case there is a need, the backup path can be activated bysending a control frame along the primary RSTP path indicating to theparticipating nodes to switch to the backup paths.

FIG. 3 illustrates a system 10′ as an alternative preferred embodimentto system 10 described above, where system 10′ has certain similaritiesbut also differs in various respects as appreciated by one skilled inthe art given the following. For sake of presenting a comparableillustration, system 10′ includes the same number of nodes N₁ through N₇shown above in FIGS. 1 a, 1 b, and 1 c. However, in system 10′, a totalof three different sets of logic links are shown, where each set isdistinguished in the Figure by using a different type of lines.Specifically, a first set of logic links is shown with solid linesbetween various nodes, a second set of logic links is shown with dashedlines between various nodes, and a third set of logic links is shownwith dotted lines between various nodes. The specific connections ofeach different set are as shown in the following respective Tables 4, 5,and 6:

TABLE 4 (solid line links) node connected to by port N₁ N₂ P1₁ N₁ N₇ P1₃N₂ N₁ P2₁ N₂ N₃ P2₂ N₂ N₅ P2₃ N₂ N₆ P2₄ N₃ N₂ P3₁ N₃ N₄ P3₂ N₄ N₃ P4₁ N₅N₂ P5₁ N₆ N₂ P6₃ N₇ N₁ P7₁

TABLE 5 (dashed line links) node connected to by port N₁ N₂ P1₁ N₁ N₇P1₃ N₂ N₁ P2₁ N₂ N₃ P2₂ N₃ N₂ P3₁ N₃ N₅ P3₃ N₄ N₅ P4₂ N₅ N₃ P5₂ N₅ N₄P5₃ N₆ N₇ P6₁ N₇ N₁ P7₁ N₇ N₆ P7₂

TABLE 6 (dotted line links) node connected to by port N₁ N₆ P1₂ N₂ N₆P2₄ N₂ N₅ P2₃ N₃ N₅ P3₃ N₄ N₅ P4₂ N₅ N₂ P5₁ N₅ N₃ P5₂ N₅ N₄ P5₃ N₆ N₇P6₁ N₆ N₁ P6₂ N₆ N₂ P6₃ N₇ N₆ P7₂

In general, each set of paths alone is comparable in some respects to aprior art spanning tree; however, collectively and individually thepaths in FIG. 3 are distinguishable from the prior art for variousreasons, some of which are also detailed later. As one distinction, inthe preferred embodiment, each different set of links in system 10′ isidentified (i.e., pre-computed) statically given the network topologyand prior to the time of a network failure in system 10′, where thiscomputation may be manual or automatic and where various algorithms canbe used and traffic engineering rules also may be incorporated makingthis scheme very amenable for Traffic Engineering. Also in connectionwith a preferred embodiment, preferably the sets in their entirety arelink disjoint, that is, no single link between two nodes is served byall sets of connections. Thus, in the example of FIG. 3 where three setsof connections are provided, then no single link between any of thenodes is connected by all three of those sets. Given these preferences,the benefits and operation with respect to the various sets of links areas discussed after the following discussion of a preferred packet formatfor system 10′.

FIG. 4 illustrates a packet format 20′ according to an alternativepreferred embodiment and for use in system 10′ of FIG. 3. Packet 20′includes five fields. A first field 20′₁ indicates the address of theingress edge node in system 10′. Thus, field 20′₁ identifies the addressof the first node in system 10′ that encounters packet 20′ once packet20′ is provided by an external source to system 10′. A second field 20′₂indicates the address of the egress edge node for packet 20′. In thisregard, note that Ethernet bridge networks provide sufficient controlssuch that when a packet is received external from the network, itincludes a source and destination address as relating to nodes externalfrom the network; in response and in order to cause the packetultimately to be directed to the packet-specified destination address,the ingress edge node determines a desired egress edge node withinsystem 10′ such that once the packet arrives at that egress node, it cantravel onward to the external destination MAC address. According to apreferred embodiment, the ingress edge node locates within packet 20′both its own address, shown as field 20′₁, as well as the egress edgenode address, shown as field 20′₂.

Continuing with FIG. 4, a third field 20′₃ is indicated as a link setfield. As further detailed below, link set field 20′₃ is an M-bit fieldthat can specify any one of up to 2^(M) different sets of links inconnection with system 10′, where each link set represents one of thesets of links in FIG. 3. Further, link set field 20′₃ could be providedas an addition to existing Ethernet frames or, alternatively, it couldbe one or more bits that are already in the Ethernet frame yet where thefunction of that bit or bits is changed to be consistent with thefunctionality described in this document as relating to link set field20′₃. In the present example of system 10′ which has three sets oflinks, then M=2. Accordingly and by example, assume that a setting equalto 00 (binary) in tree field 20′₃ indicates that the packet is to berouted along the solid line set of links in FIG. 3. Further and asdetailed later, a different value in link set field 20′₃ therebyrepresents a different set of links in FIG. 3, so to complete theexample, assume that a setting equal to 01 (binary) in link set field20′₃ indicates that the packet is to be routed along the dashed line setof links in FIG. 3, and assume that a setting equal to 10 (binary) inlink set field 20′₃ indicates that the packet is to be routed along thedotted line set of links in FIG. 3.

Continuing with FIG. 4 and completing the remaining fields, a fourthfield 20′₄ is indicated as an R-bit, which has a state that permitseither re-routing or dropping of the packet, as detailed later.Additionally, packet 20′ includes a payload field 20′₅. Payload field20′₅ includes the packet as originally transmitted from the node that isexternal to system 10′. Note, therefore, that this filed 20′₅ includesthe user data as well as the originally-transmitted external sourceaddress and destination address, where those addresses are directed tonodes outside of system 10′. Thus, field 20′₅ includes the sameinformation as discussed in connection with packet 20 of FIG. 2, withthe exception of not including link type field 20 ₅. Accordingly, packet20′ includes two sets of addresses, one (in field 20′₅) pertaining tothe source and destination node addresses that are external from system10′ and the other (in fields 20′₁ and 20′₂) identifying the ingress andegress edge nodes in system 10′. This technique may be referred to asencapsulation or MAC-in-MAC encapsulation in that there is one set ofMAC addresses encapsulated within another set of MAC addresses. Lastly,note that when packet 20′ reaches its egress edge node N_(x), that nodestrips fields 20′₁, 20′₂, 20′₃, and 20′₄ from the packet and thenforwards, to the destination address node in payload field 20′₅, theremaining payload field 20′₅ as the entirety of the packet. Thus, uponreceipt of the final packet at a node external from system 10′, thedestination node is unaware of the information previously provided infields 20′₁, 20′₂, 20′₃, and 20′₄.

The operation of system 10′ of FIG. 3 is now discussed in connectionwith frame format 20′ of FIG. 4. Prior to any failure in any of the linksets in system 10′, each different link set is identified as a viablecommunication path for packets, as set forth above. Thereafter, networkcommunications commence through system 10′. Under normal operatingconditions when no failure has been detected in system 10′, then eachpacket will have a same setting in its link set field 20′₃. This samesetting provides an indication that the packet should be routed along asame one of the different sets of links in FIG. 3. For example, assumethat a setting equal to 00 in link set field 20′₃ indicates that thepacket is to be routed along the solid line set of links in FIG. 3.Further and as detailed later, a different value in link set field 20′₃thereby represents a different set of links in FIG. 3, so to completethe example, assume that a setting equal to 01 in link set field 20′₃indicates that the packet is to be routed along the dashed line set oflinks in FIG. 3, and assume that a setting equal to 10 in link set field20′₃ indicates that the packet is to be routed along the dotted line setof links in FIG. 3. Thus, under normal operating conditions and withouta link failure in system 10′, only a single one of these settings isused, so assume that all packets include a value of 00 in theirrespective link set field 20′₃. When a node in system 10′ receives sucha packet at a receipt port, the node consults a routing table todetermine a transmit port for the packet. In a preferred embodiment,this routing table differs in association from both the forwarding tableof the spanning tree prior art (i.e., Association 1) and the bypasstable of system 10 (i.e., Association 2). Specifically, in system 10′,the routing table in a given node identifies, for each different set oflinks, the other nodes within system 10′ that are accessible by eachport of the given node. For example, such a table for node N₁ preferablyrepresents the following information:

TABLE 7 link accessible via set node(s) port 00 N₇ P1₃ 00 N₂, N₃, N₄,P1₁ N₅, N₆ 01 N₂, N₃, N₅ P1₁ 01 N₇, N₆ P1₃ 11 N₆, N₇, N₂, P1₂ N₅, N₃, N₄As shown by way of example in Table 7, the association of the routingtable of system 10′ is as shown in the following Association 3:link set and egress node within system 10′→transmit port  Association 3

To further appreciate the operation of system 10′ and with respect toAssociation 3, assume as an example that node N₁ receives a packet withits link set field 20′₃ set to 00. Further, recall from FIG. 4 that inthe preferred embodiment of system 10′, that packet also will includeMAC-in-MAC encapsulation, that is, it will include both the externaldestination MAC address in payload field 20′₅, but it also will includethe egress node MAC address in field 20′₂, that is, a destination nodewithin system 10′. Given this information, then node N₁ chooses itsappropriate transmit port. Continuing then with an example wherein thepacket has its link set field 20′₃ set to 00, assume further that theegress node for the packet is stated in field 20′₂ to be node N₅;accordingly, from Table 7 and Association 3, then node N₁ will transmitthat packet out its port P1 ₁. This packet will therefore next bereceived by node N₂, and node N₂ responds in a comparable manner.Specifically, since the packet still has its link set field 20′₃ set to00, then node N₂ will consult its own routing table to identify, forlink set 00 (i.e., solid lines in FIG. 3), which of its ports maytransmit the packet toward node N₅, and from FIG. 3 it will beappreciated by one skilled in the art that port P2 ₃ will be soidentified. Hence, the packet is transmitted by node N₂ to node N₅ alonglink set 00. Next, node N₅ will receive the packet from node N₂ anddetermine, from field 20′₂, that it is the egress node for the packet.Accordingly, node N₅ removes fields 20′₁, 20′₂, 20′₃, and 20′₄ from thepacket and then communicates just field 20′₅, as the entirety of thetransmitted packet, to a node external from system 10′. At this point,therefore, the packet has been successfully routed through system 10′and then transmitted to a node external from system 10′, which will beunaware of the routing steps and fields that were otherwise used bysystem 10′ for such routing.

Continuing with the operation of system 10′, assume next that a failureoccurs in one of the illustrated links of FIG. 3. For example, assumethat a failure occurs between nodes N₁ and N₂. Once again using knownprotocols, the various nodes in system 10′ will become aware of thefailure. In response, a node may change the setting in link set field20′₃ of a packet so as to route the packet around the failure, where thespecific node that makes the change is dictated in one preferredembodiment by the state of the bit in R-bit field 20′₄. Particularly, inone preferred embodiment, when R=0, then only the ingress node in system10′ is permitted to change the setting in link set field 20′₃, whereasif R=1, then the node adjacent the failure changes the setting in linkset field 20′₃. Note, also, therefore, that if R=0 in a packet receivedby a node adjacent a failure, and the link set field 20′₃ of that packetidentifies a path that includes the failed link, then the packet will bedropped by the receiving node. Another use of R-bits is to emulate TTL(time-to-live) in the case of multiple switching between the link setsupon multiple link failures (i.e., they determine how many link sets apacket can be switched before the packet is dropped by an intermediatenode). In any event, in the present example, assume that R=0. Thus,continuing with the present example, assume that node N₁ receives apacket from a node external from system 10′. First, since node N₁ istherefore the ingress node in this example, it will append the fields20′₁, 20′₂, 20′₃, and 20′₄ to the packet to create the format 20′ ofFIG. 4. Additionally with respect to field 20′₃, recall from above thattypically a default setting of link set field 20′₃ equal to 00 isimplemented. However, the identified failure between nodes N₁ and N₂will be known to node N₁, in view of the known network topology, toaffect link set 00. Indeed, in this case the link failure affects linkset 01 (i.e., the dashed line link between nodes N₁ and N₂).Accordingly, node N₁, as the ingress node and because R=0, sets thestate of link set field 20′₃ to a value that represents a link set thatis still completely intact, that is, along which no failure hasoccurred. In the present example, the only remaining such link set islink set 10 (i.e., the dotted line links in FIG. 3). Thereafter, node N₁routes the packet in the same manner as described above in the exampleof routing on link set 00, but now this packet is routed along link set10. Thus, node N₁ consults its routing table to identify the Association3 for the present packet. Assume in the present example that the egressnode, as identified in field 20′₂ of the packet, is node N₄.Consequently, node N₁ determines that for link set 10, node N₄ isaccessible via port P1 ₂ and, thus, node N₁ uses that port as itstransmit port for the packet. Next, node N₆ receives the packet, and ittoo consults its routing table, with reference to the nodes accessiblefor link set 10; from that analysis, node N₆ will identify its port P6 ₃as a transmit port to node N₂. Note, therefore, that node N₂ willreceive the packet from node N₆, thereby having avoided the failure tolink sets 00 and 01 between nodes N₁ and N₂. After N₂ receives thepacket, it too will consult its routing table with reference to link set10 and the egress node of N₄, thereby transmitting the packet at itstransmit port P2 ₃ to node N₅. Similarly, node N₅ will consult itsrouting table with reference to link set 10 and the egress node of N₄,thereby transmitting the packet at its transmit port P5 ₃ to node N₄.Accordingly, node N₄, as the egress node and as ascertained from field20′₂, removes fields 20′₁, 20′₂, 20′₃, and 20′₄ from the packet and thencommunicates just field 20′₅, as the entirety of the transmitted packet,to a node external from system 10′.

Some additional observations with respect to system 10′ are noteworthy.As a first observation, note that when a failure occurs, because eachlink set is identified prior to that time, then packet communicationsmay be quickly switched to a different link set without awaitingdetermination of new routing information. As a result and as a secondobservation, there is not the time expenditure that is required in theprior art RSTP systems where each node is required to flush itsforwarding table and then re-learn a new single route. In other words,the routing databases are not corrupted due to a change in link status.As a third observation, while system 10′ is shown to include threealternative link sets, any different number of pre-computed link setsmay be implemented, where the value of M-bits in field 20′₃ is adjustedto accommodate the total number of such sets. As a fourth observation,like system 10 described earlier, system 10′ also may emulate 1+1 and1:1 protection for certain applications. As a fifth observation, notethat in the prior art there is a protocol identified by the nameMultiple Spanning Trees (i.e., 802.1s), where there are multiplespanning trees, but no switching between them is possible because a VLANcan be registered on only one spanning tree and therefore cannot beswitched. In contrast, in the preferred embodiments described relativeto FIGS. 3 and 4, it is contemplated to have VLAN registered on manydifferent set of links, where each such set is in part comparable to adifferent spanning tree, but in the preferred embodiment this therebypermits switching between them without re-registration, in contrast tothe above-described prior art where such switching is not permitted. Asa sixth observation, system 10′ is described above as switching trafficto a different link set following a failure along a previous link set.In one approach, however, the previous link set may be established as adefault link set that, upon a failure in that set, re-converges using aprotocol comparable to that of the prior art, but while thatre-convergence is occurring, traffic is already routed along a differentlink set by changing the value in link set field 20′₃ accordingly.Thereafter, when re-convergence is complete, the value in each packetlink set field 20′₃ may be changed again, now to a value that identifiesthe newly re-converged link set. In this sense, therefore, some of theadditional link sets are pre-configured statically, while the defaultlink set re-converges dynamically after a failure in that link set. As aseventh observation, note that M, that is, the number of bits in linkset field 20′₃, in one embodiment may be equal to one, whereas above Mis shown by way of example as greater than one. In the case when M=1,there are therefore only two different routing link sets and for ageneral topology it is impossible to find two completely link-disjointlink sets in this regard—however, the instance of M=1 still may be usedto provide protection to selected links. As a final observation, notethat in lieu of the use of link set 20′₃ to indicate the set of linksalong which packets are to be communicated, a broadcast packet could besent, indicating to certain nodes, that thereafter all packets are to becommunicated along a desired set of links. In other words, thisbroadcast packet could present to those nodes an identifier in a mannercomparable to that described above with respect to the value set forthin link field 20′₃. Thus, initially a default set of links could beidentified with such a broadcast packet, whereupon all packets arethereafter communicated along that default set of links; thereafter,upon a failure in the default link set, a new broadcast packet would becommunicated, indicating an alternative set of links, whereupon allpackets are thereafter communicated along that alternative set of links.This process can continue to identify additional sets of links, wherethose link sets are either newly identified after a link failure (e.g.,re-convergence) or for link sets that are pre-computed at a time priorto the failure.

From the above illustrations and description, one skilled in the artshould appreciate that the preferred embodiments provide bridged networksystem in which traffic resiliency is provided by quickly switchingtraffic to a pre-identified route upon a link failure. Further in thisregard, various alternatives have been described, including examplesillustrated by systems 10 and 10′. Both of these systems provide abridged network, wherein upon a failure within the bridged network alonga first set of links within the network, traffic is routed to a secondand different set of links where the second set is identified eithermanually or automatically prior to the time of the failure, and wherethe second set switch is in response at least in part to a routeindicator field in the packet. In system 10, the route indicator fieldis a link type field 20 ₅, operable to indicate that the packet is tocontinue along a spanning tree route or a bypass route. In system 10′,the route indicator field is a link set field 20′₃, operable to indicatethat the packet is to continue along a first set of links forming afirst route, a second set of links forming a second route, and so forthfor up to 2^(M) sets of links corresponding to a respective number of2^(M) routes. In this manner, the time to switch traffic from the firstto second path is reduced as compared to the prior art RSTP systems. Inthe approach of system 10, following the switch to the second set oflinks, which in that case is a bypass set of links, a third set of linksmay be established using RSTP protocol, that is, a flush and re-learnmay be performed while traffic continues along the second (bypass) setof links. During this re-learn period, traffic is permitted to occurover the bypass links as is achieved by changing the state of a linktype field 20 ₅ of the packet and in connection with a bypass table thatuses an Association 2 described above. Once the third set of links isestablished and properly located in the routing tables of the nodes ofsystem 10, packet flow may be routed to the third set of links and areturn to the use of Association 1 occurs, thereby leaving the secondset as a possible bypass route should the third set of links alsoexperience a failure. In the alternative approach of system 10′, asufficient number of link sets are preferably identified prior to anyfailure, and after such a failure then packets may be routed to any oneof the link sets that is not affected by the failure, where thisalternative routing is achieved by changing the state of a link setfield 20′₃ of the packet and in connection with a routing table thatuses an Association 3 described above. Given the preceding, one skilledin the art should appreciate numerous aspects of the present preferredembodiments. Further, while the present embodiments have been describedin detail, various substitutions, modifications or alterations could bemade to the descriptions set forth above without departing from theinventive scope. For example, the number of nodes or link sets describedabove may be altered. As another example, the manner of programming thedescribed functionality into the various nodes may be achieved invarious different approaches. As still another example with respect toFIG. 4, note that in some instances R-bit field 20′₄ may be eliminatedin order to achieve a level of flexibility of implementation or it maybe optional. In other words, where R-bit field 20′₄ is not available,then only switching by the node adjacent to the failed link is allowedin the network, and therefore there is no need for R-bit field 20′₄.Still further examples may be ascertained by one skilled in the art.Consequently, the above is intended as illustrative but not exhaustive,and therefore these examples as well as the preceding teachings furtherdemonstrate the inventive scope, as is defined by the following claims.

1. A bridged network system, comprising: a plurality of nodes; whereineach node in the plurality of nodes is coupled to communicate with atleast one other node in the plurality of nodes; wherein the plurality ofnodes comprise a bridge network between external nodes locatedexternally from the plurality of nodes; and wherein each node of theplurality of nodes is operable to perform the steps of: receiving apacket, wherein the packet comprises a route indicator field furthercomprising one or two bits that indicates a route; responsive to thepacket being received prior to a time of failure along a communicationlink between two of the plurality of nodes, transmitting the packetalong a first route in the system to another node in the plurality ofnodes; and responsive to the packet being received after a time offailure along a communication link between two of the plurality of nodesand in response to a change of state of the one or two bits in the routeindicator field to indicate an alternate route should be used as aresult of a link failure, accessing an internal bypass table to retrievea second route and transmitting the packet along the second route in thesystem to another node in the plurality of nodes, wherein the secondroute differs from the first route and is stored prior to the time offailure and wherein the change of state of the one or two bits isperformed by one of the nodes that is responsible for detecting the linkfailure and for receiving and transmitting the packet.
 2. The bridgednetwork system of claim 1 wherein the packet comprises a first packetand wherein each of the plurality of nodes is further operable toperform the steps of: determining a third route in the system after thetime of failure; receiving a second packet after the first packet; andtransmitting the second packet along the third route to another node inthe plurality of nodes.
 3. The bridged network system of claim 2, andfurther comprising after the step of receiving the second packet andprior to the step of transmitting the second packet, a step of changinga state of the route indicator field to cause transmission to the thirdroute.
 4. The bridged network system of claim 3 wherein the step oftransmitting the packet along a first route comprises: identifying atransmit port in the node that corresponds to a destination address inthe packet, wherein the destination address corresponds to a nodeexternal from the plurality of nodes; and transmitting the packet viathe transmit port to the first route.
 5. The bridged network system ofclaim 4 wherein the step of transmitting the packet along a third routecomprises: identifying a transmit port in the node that corresponds to adestination address in the packet, wherein the destination addresscorresponds to a node external from the plurality of nodes; andtransmitting the packet via the transmit port to the third route.
 6. Thebridged network system of claim 2 wherein the receiving step comprises anode, adjacent to a failure in the first route, receiving the secondpacket.
 7. The bridged network system of claim 2, and further comprisingafter the step of receiving the second packet and prior to the step oftransmitting the second packet, a step of setting a value of a routeindicator field in the second packet to cause transmission to either thefirst or second route.
 8. The bridged network system of claim 1 whereinthe step of transmitting the packet along a second route comprises:identifying a transmit port in the node that corresponds to a receiptport in the node; and transmitting the packet via the transmit port tothe second route wherein the packet is a data packet.
 9. The bridgednetwork system of claim 8 wherein the transmitting step is notresponsive to a destination address within the packet.
 10. The bridgednetwork system of claim 1 wherein multiple ones of the plurality ofnodes are operable to receive and transmit the packet along the secondroute until the packet reaches an egress node in the plurality of nodes.11. The bridged network system of claim 10 wherein the transmission byeach node in the multiples ones of the plurality of nodes: identifying atransmit port in the node that corresponds to a receipt port in thenode; and transmitting the packet via the transmit port to the secondroute.
 12. The bridged network system of claim 1: wherein a first nodein the plurality of nodes that receives a packet from a first externalnode of the external nodes located externally from the plurality ofnodes comprises an ingress node; wherein a second node in the pluralityof nodes that is coupled to communicate the packet to a second externalnode of the external nodes located externally from the plurality ofnodes comprises an egress node; and further comprising a step of,responsive to a node in the plurality of nodes receiving a packet as aningress node, insetting an address of the ingress node and the egressnode into the packet.
 13. The bridged network system of claim 12:wherein the step of transmitting the packet along either the first routeor the second route comprises: identifying a transmit port in the nodethat corresponds to the address of the egress node in the packet; andtransmitting the packet via the transmit port to either the first orsecond route.
 14. The bridged network system of claim 13 wherein thestep of transmitting the packet along either the first route or thesecond route is further responsive to the route indicator field in thepacket to cause transmission to either the first route or the secondroute, respectively.
 15. The bridged network system of claim 14 whereinthe packet further comprises a field for indicating allowability of aningress node or a node adjacent a failure to change a state in the routeindicator field.
 16. The bridged network system of claim 12 wherein thefirst route and the second route are routes in a plurality of differentroutes, wherein each route in the plurality of different routes isidentified prior to the time of failure.
 17. The bridged network systemof claim 16 wherein each route in the plurality of different routes isidentified by a corresponding and different value in the route indicatorfield.
 18. The bridged network system of claim 16 wherein the packetfurther comprises a VLAN identifier field operable to identify eachdifferent route in the plurality of routes so as to facilitate abroadcast message to all nodes on an identified route.
 19. The bridgednetwork system of claim 18 wherein the VLAN identifier field facilitatesregistration of selected different routes in the plurality of routes.20. The bridged network system of claim 16 wherein the packet comprisesa first packet and wherein each node of the plurality of nodes isfurther operable to perform the steps of: determining a third route inthe system after the time of failure; receiving a second packet afterthe first packet; and transmitting the second packet along the thirdroute to another node in the plurality of nodes.